unlist strips date class

Hi,

Is this a bug?

unlist(list(as.Date("2015-01-01")))

[1] 16436

Good question.

More generally one might reasonably expect 'unlist(x)' to be equivalent
to 'do.call(c, x)' on a list 'x' where all the list elements are atomic
vectors:

   x <- list(1:3, letters[1:2])
   unlist(x)
   # [1] "1" "2" "3" "a" "b"
   do.call(c, x)
   # [1] "1" "2" "3" "a" "b"

However, if the list contains dates:

   x <- list(as.Date("2015-01-01") + 0:2, as.Date("2016-12-02"))
   unlist(x)
   # [1] 16436 16437 16438 17137
   do.call(c, x)
   # [1] "2015-01-01" "2015-01-02" "2015-01-03" "2016-12-02"

then 'unlist(x)' drops the attributes and 'do.call(c, x)' does not.

And if the list contains factors:

   x <- list(factor("Z"), factor(c("a", "Z", "b")))
   unlist(x)
   # [1] Z a Z b
   # Levels: Z a b
   do.call(c, x)
   # [1] 1 1 3 2

then it's the other way around. Also note that the fact that the first
2 numbers in the result of 'do.call(c, x)' are the same is
confusing/misleading. Hard to see how this result could be useful
to anybody.

These inconsistencies might well be documented but hopefully they can
be addressed.

Cheers,
H.

Herv? Pag?s

Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
P.O. Box 19024
Seattle, WA 98109-1024

E-mail: hpages at fredhutch.org
Phone:  (206) 667-5791
Fax:    (206) 667-1319